If you don't go into debt to buy a house, either you rent or you live on the street. Someone has to own the house, and chances are there will be some debt attached.
So in aggregate how many people would take out mortgages the year that somebody institutes a policy that guarantees constant deflation for the foreseeable future? After that date, who would ever take out a mortgage? How bout the aggregate level of debt in the entire economy? It crashes.
To be even more explicit the correct theoretical cost for loans to be enticing to apply for would be at
negative interest rates. this is where the credit market equilibrium would be achieved.
Unfortunately, the banks would think to themselves a) should I loan this random person $100,000 and get back less than $100,000 in the future or b) just hoard the $100,000 and be guaranteed to still have $100,000 which will be worth double in real value in 24 years?